Process of making reenforced hard rubber



Patna-a a; so, 1928.

UNITED STATES LATEX RESEARCH CORPORATION, 01' MASSACHUSETTS.

PATE T OFFICE,

WILLIAM BURTON wnsco'rr, or BOSTON, massacnvsa'r'rs, ASSIGNOR T THERUDBEIB.

or BOSTON, massxcnusar'rs, A CORPORATION PROCESS OI MAKING REENEORCEDHARD RUBBER.

1W0 Drawing. Original application filed November 18, 1922, Serial'No.601,910. Divided and thin application filed December 23, 1926. Serial30. 156.764.

This invention relates to reenforced hard rubber and process of makingthe same: and it comprises an article of ebonite or hard rubberstrengthened and reenforced by con- 5 tained distributed long vegetableor mineral fiber therein, such fiber being usually cottoii and suchrubber extending into and permeating the fiber; and it further comprisesa method of producing such a reenforced hard rubber article whereinfinely divided hard rubber is admixed with finel -divided partially*cured rubber, such as bu gs, sulfur and relatively'long fibers and themass moistened with a solution of latex, dried,

shaped and vulcanized; all as more fully hereinafter set forth and asclaimed.

, The present invention relates to the,pr0-

duction of hard rubber articles containing distributed reenforcing fiberof substantial 2 length, the rubber permeating the fiber. The

hard rubber may; occur merely in the quantity requisite to serve as abonding means in making articles of granular material; and particularlyabrasive articles. This, however, I do not herein specifically claim, it

forming the subject matter of another and copending application, SerialNo. 601,910,v

filed November 18, 1922, whereof the present application is a division.

In the usual compounding of rubber to make such materials as hardrubber, the rubber and the compounding ingredients added thereto are miled together. Where the filleris finely divided as in the case ofwhiting, zinc oxid, etc., the millingaccomplishes the desired result;but the situation is different whenfcompounding' ingredients of acoarser nature are to occur in the final products and the comminutiontaking place 40 in the milling is undesirable. In particular theexigencies of milling'preclude the use of fiber of efiective length as areenforcing and strengthening ingredient. Fiber is extremely desirablein such compositions for reenforcing and toughening; but milling breaksup and disintegrafes it. Anyfiber added to the composition and milledtherewith, t0 the extent.'necessary to produce uniform distribution isdisintegrated and reduced to extremely short lengths. Heretofore theonly practicable way of incorporating long fiber or other comparativelycoarse mgredients' into rubber compositions of any kind has been the useof the so-called rubber solutions, and these are not only unsatisfactorybut,

because of the solvents necessarily used, are

tions containing distributed fiber in minor.

proportions and in random arrangement. It is one object of thisinvention to produce hard rubber articles containing distributed fibersof substantial length" and in random arrangement in a simple and readymanner, witheconomies in the use of material and safety in operation. Q

In making my composition I take advantage of the properties of latex orrubber emulsions containing the caoutchou'c of latex. Latex is the milkysap of variousplants and can be obtained carrying as high as 20 to 30per cent,of caoutchouc. Whetherthis caoutchouc as it is contained in thelatex emulsion is the same chemicall as the ordinary caoutchouc of rawrub er is an undecided question. For the present purposes it isconvenient to call it by that name. Latex readily coagulates or clots,with production of ordinary raw rubber as a reticulated or vein'edcoagulum; the coagulum not being homogeneous. Acids, creosote andvarious other chemicals produce coagulation; and coagulation even takesplace on mechanical agitation. Latex can, however, be shielded againstcoagulation by the presence of various stabilizing chemicals, mostly ofan alkaline nature. Ammonia is the most convenient stabilizer. Variouspurified and concentrated standardized preparations having theproperties of rubber emulsions or caoutchouc emulsipns may be made fromlatex by narylatex, stabilized with a little alkali, or

the stated similar purer uncoagulated standardized preparations madetherefrom.

On drying down, latex at first gives-a gel, this gel formation beingirreversible, and

milled rubber than like raw rubber.

In the present invention, in lieu of milling or grinding together thematerials which areto be compounded in making hard rub-- ber, I simplymix them and incorporate sufiicient latex or the latex preparationsmentioned to act as a bonding agent, dry, shape and vulcanize. Ondrying, the latex yields I get-her and uniting the several ingredients.

As will be observed, in operating in this'way it is possible toincorporate any desired amount of any desired fiber; no milling orvlong-continued mechanical working being necessary.

Operating in this way, I am also enabled 3 to use various waste rubbermaterials as sub-v stantial components such as hard rubber waste, rubberbullings, etc., with substantial economies in operation. Onvulcanization these materials, together with the latex caoutchouc,- areconverted into an integral mass of hard rubber.

In practicing my invention, I ordinarily employ a large roportion, say,30 per cent or so, of hard ru ber waste reduced to a fine state.Bulfings may be employed. With this .I admix a certain amount of finelydivided rubber in which the curing has not been carried to completion.Bulfings from partially cured articles may be used. The amount of' thispartially cured rubber may be around 30 per cent. With these two gradesof rubber, I admix sulfur in excess of the amount I required for hardvulcanization and also such an' amount of fiber as I maydeemdesirable inth e finished article. Disintegrated rubber-frictioned cotton fabric asproduced in the usual process of reclaiming rubber from old tires andthe like may be used. It

. carries both longefiber and partially cured rubber and may usedwithout an addition of hard rubber.

. y In making my mix, since the othermatev rials are present as finelydivided particles,-

no difficulty arises in the incorporation of fiber in any. amount and ofany character. Admixture may be dry or wet. Int-he latter event, I uselatex or a dilution thereof. Because of the penetrating nature of latex,it is practicable to apply the undiluted latex directly to a wet pulp orbody of the other ingredients. I rarely use more latex than wouldcorrespond to about 5 per cent latex caoutchoucin the final hard rubber.The mixture 'isordinaril dried to convert the latex solids into ge isthen further sub the unitaryhard rubber mass permeates the fiber in sofar as this fiber is 'open or porous in texture. Compositions made as sofar described without the use of special fillers are 'intergranularfilms of dried gel bonding t0*"particularly adapted forsuch severe usesas battery jars and plates, separator plates, electrical insulations,panels, etc.

For some uses, a certain amount of filler may be admixed with thecomposition produced as so far described; this filler being any of thoseusually employed in compounding hard rubber. Sometimes the presence ofthis filler is desirable; sometimes not.

In the present invention I have devised a method of producing hardrubber in which the physical characteristics of the coarse compoundedingredients are not injured as is the case in the ordinary millingtreatments. This invention is useful in the production of many otherarticles and is not limited in this respect to articles containingfiber, although in most embodiments of my invention Iuse more or lessreenforcing fiber. The reenforcement fiber is particularly useful instrengthening and toughening the hard rubber, whether the hard rubber beused as a molded article by itself or as a bonding means for otherthings. It lessens the tendency of the rubber to shatter, crack, pit andfissure under bending strains. One particularly useful field for thepresent invention is in the manufacture rubber bonded abrasives,

as set forth in detail in my stated copending application, Ser. No.601,910.

'In the manufacture of rubber, bonded abrasives, the grains of abrasivesare usually milled with and into the rubber. This is not only hard onthe milling rolls but also tends to shatter, disintegrate and dull orround the abrasive grains themselves. In milling, the grains abrade eachother, dulling and rounding their cutting or abrasive no injuryof theabrasive grains occurs, and the finished product contains the chosensize grains only and is, in consequence, uniform in its action and isrelatively free cutting. In making such articles, I customarily usefiber in the rubber. In abrasive Wheels and similar articles, the addedtoughness and strength given by fiber in the hard rubber areparticularly advantageous. As the abrasive material, I may use any ofthe ordinary abrasive materials, such as carborundum, alundum,siloxicon, corundum, silica, natural emery, garnet, etc.

In making these and other fiber reenforced hard rubber composition underthe present invention, I usually employ about equal .parts of hardrubber dust and of bufiings from incompletely vulcanized rubber. Forreenforcing purposes, 5 per cent of cotton fiber is usuallysatisfactory. There should be enough sulfur to hard cure the latexrubher and the partially cured rubber. In using fibrous material fromrubber reclaiming, the rubber and fiber are both utilized. In lieu ofthe cotton fiber I may, of course, use any lution may, of course, beused directly in making the mixture. The Water is dried out to convertthe latex into a dry gel and the composition heated and compacted, witha final heating under vulcanizing conditions appropriate for convertingall the rubbery materials into hard rubber. Such a composition as justdescribed makes a good battery plate and is useful for many otherpurposes because of the toughness imparted by the long fiber. Even asmall amount of long fiber incorporated into the hard rubber in themanner described gives a highly advan- 'tageous resistance to breakingand cracking under bending stresses. The hard rubber does not shatter orbreak readily.

As stated, any ordinary vegetable or mineral fibers may be usedinpracticing the process of the present invention, provided the fibers aresufficiently long to give a reenforcing action. In the case of asbestos,it is often' desirable or necessary to purify it before use.

This is not, however, ordinarily necessary with vegetable fibers.

What I claim is In the manufacture of articles composed of or comprisinghard rubber, the process which comprises admixing comminuted hardrubber, disintegrated partially cured rubber, sulfur, fiber and rubberlatex, dryi g, molding and vulcanizing.

In testimony whereof, I have hereunto affixed my signature;

WILLIAM BURTON WESCOTT.

